Helmet fitting and impact attenuation system

ABSTRACT

There is provided a safety helmet with a helmet fitting and impact attenuation system. The system comprises a semi-rigid space frame attachable to the safety helmet and a headband, releasably attachable to one or more arms of the space frame. The space frame and headband accommodate the use of an impact attenuation liner mounted between the space frame and the helmet shell. The helmet fitting and impact attenuation system also may be used to update and retrofit existing helmet shells.

RELATED APPLICATION

This application claims the benefit under Title 35, U.S.C., S. 119(e) of U.S. Provisional Application No. 61/014,239 filed on Dec. 17, 2007, which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a safety helmet fitting and impact attenuation system and a safety helmet fitting and impact attenuation system that may be retrofitted to existing helmet shells.

BACKGROUND OF THE INVENTION

Modern safety helmets must fulfill a number of functions for the helmet wearer. The helmet must provide protection from any one or combination of blast, debris, projectile or impact as a result of striking an object or being struck by an object; support the mounting and use of additional devices worn on or near the head or helmet, such as various types of glasses, goggles, communications devices, microphones and other devices; and provide a comfortable fit and ventilation for the wearer without comprising the other functions.

To illustrate an embodiment of the invention, a military helmet shall be used in the description. For military applications, helmet design is further limited in the choice of materials, fasteners and space that can be used to meet these design goals and create a helmet that functions in harsh environments.

A safety helmet typically is comprised of layers of components to provide comfort, fit and impact protection. A hard helmet shell at the outside layer provides protection from blasts, impact, ballistics and debris. Interior to the shell, a crown webbing layer, a headband and straps comprise the helmet suspension and retention systems which must provide for proper retention, fit and placement of the helmet on the wearer. An impact attenuation liner or material also may be present to further protect the wearer against impact.

Within traditional helmet suspension systems, an interior crown webbing layer provides for outward displacement of the helmet shell relative to the wearer's head.

An example of a previous helmet design, which is shown in FIGS. 1 and 2, is Canadian military helmet model CG 634. In this previous design, intricate crown webbing was used to provide proper spacing between the wearer's head and the helmet shell. Typically, the crown webbing layer is attached to an annular band which is attached to the helmet shell at three or four permanent mounting points, depending on the design of the shell. In the helmet shown in FIG. 2, two mounting points are provided at the front sides of the helmet and a single mounting point is located at the back-center of the helmet.

A further headband layer provides fit and support of the helmet and is adjustable, for example via Velcro™, to adapt to different head circumferences. The headband is affixed to the annular band through multiple loops of crown webbing which allow for adjustment of the headband or removal and replacement of a headband. The crown webbing layer also may be adjusted to the wearer's head via a drawstring. Although existing helmet designs provide for some adjustment of the crown webbing layer, the webbing loops and drawstring are known to create pressure points and cause discomfort for the wearer.

Adjustable retention straps typically extend from the permanent mounting points on the helmet shell to affix the helmet to the wearer. Straps extending between the back and respective front side mounting points further provide stability for the helmet. The straps typically are joined under the wearer's chin, which is supported by a chin cup, to securely retain the helmet against the wearer's head. In some helmets, a further nape strap is provided at the back mounting point to separate the attachment of the straps at the back and increase the stability of the helmet. Although the nape strap may increase stability of the helmet on the wearer's head, it also may provide a further source of discomfort, pressure and fit problems for the helmet wearer.

Impact attenuation liners come in many different form factors utilizing many different materials. Current safety helmets use a combination of a webbing system offset from the helmet shell, an expanded polystyrene (EPS) foam liner and a series of foam pucks around the headband to attenuate impacts. However, other safety helmet designs use all EPS construction, some have individual pads which can be removed and repositioned for fitting purposes. The material makeup of impact attenuation liners also vary from one safety helmet to the next. These materials include but are not limited to EPS, vinyl nitrile, expanded polypropylene, polyurethane, polyethylene and engineered plastic structures. The combination of impact attenuation liner and material selection is critical to achieving a system that meets the protective requirements of the helmet as well as the fit and comfort required for prolonged use. Impact attenuating materials found in certain helmets can cause discomfort when in contact with the head due to pressure points or heat/moisture retention.

Safety helmets typically employ an impact attenuation material such as an expanded bead polystyrene (EPS) liner as a primary system to absorb blunt impacts. As well, minor attenuation may be provided by foam rubber pads situated around the circumference of the headband. However, EPS has a low chemical resistance, becomes fragile with use, and the foam rubber pads are known to be an additional cause of discomfort.

While the spacing between the helmet and the head is important for impact protection, the orientation or position of the helmet on the head is also important for stability and proper suspension and retention of the helmet. The stability and positioning of the helmet may be further affected by additional devices worn on the head or helmet, such as goggles or other eyepieces and earphones, microphones or other communications devices. Thus, once adjusted, the helmet must remain in position under static or dynamic loads. Likewise, the helmet shell, suspension system and impact attenuation liner also must not interfere with other devices worn on the head. For example, existing helmets have been found to interfere with ear pieces worn under the helmet, causing the ear piece to be displaced from the helmet wearer's ear.

Existing helmets may be fitted with an impact attenuation liner to absorb forces upon impact as described above. One or more pieces of impact attenuation material may be affixed to the helmet shell to meet this safety performance requirement. It has been found, for helmet systems with removable materials or padding, that helmet wearers also may carry out unauthorized modifications to the impact attenuation system and alter or remove the pieces of the impact attenuation material to further improve the comfort of the helmet. Such unauthorized modifications may severely impair the impact protection performance of the helmet and result in injury to the helmet wearer. Thus, comfort and proper fit of the helmet is critical to ensure unauthorized modifications do not occur which compromise the wearer's safety.

The helmet shell, impact attenuation and suspension system also must operate in harsh environments and may be degraded by sand, water and other elements. The impact attenuation, webbing and strap material typically wear out or become excessive soiled more quickly than the helmet shell, thus limiting the usable life of the helmet. A simple means to retrofit or upgrade the impact attenuation, suspension and retention system components is thus needed to allow for longer use of the helmet shell.

A further example of a safety helmet for military use is described in U.S. Pat. No. 5,068,922, issued Dec. 3, 1991 and No. 4,987,609, issued Jan. 29, 1991, to Zahn. Zahn discloses a military safety helmet with an inner supporting band, fastening strips and bosses resting against the helmet shell to provide impact protection. However, Zahn does not disclose adjustment of the inner supporting band, a second headband adjusted to the wearer, the accommodation of a liner to provide impact protection or the design of a fitting and impact attenuation system that may be used to retrofit existing helmet shells.

Thus, there is a need to improve the comfort and fit of new and existing safety helmets to accommodate additional components worn on or near the helmet, prevent wearer modifications aimed at improving fit and comfort, and to continue to meet impact protection and safety requirements during normal use.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a helmet fitting and impact attenuation system for new helmet shells or to be used to retrofit existing helmet shells. In accordance with an embodiment of the present invention, there is provided a helmet fitting and impact attenuation system for use in a helmet. The fitting and impact attenuation system comprises a semi-rigid space frame comprising a plurality of arms extending from a central crown point wherein at least three of the arms are attachable to the helmet such that the space frame is releasably fixed to said helmet. There is also provided a headband for receiving the head of a wearer, in which the headband is releasably attachable to the space frame by one or more of the arms. There is also provided an impact attenuation layer, fixably mounted to an inside surface of the helmet. The space frame maintains the headband in a fixed vertical configuration relative to the helmet.

According to another aspect of the present invention, there is provided a helmet comprising a helmet shell; a semi-rigid space frame comprising a plurality of arms extending from a central crown point wherein at least three of the arms are attachable to the helmet such that the space frame is releasably fixed to the helmet. There is also provided a headband for receiving a head of a wearer, in which the headband is releasably attachable to the space frame by one or more of the arms. There is also provided an impact attenuation layer, fixably mounted to an inside surface of the helmet shell. The space frame maintains the headband in a fixed vertical configuration relative to the helmet.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention will become apparent upon reading the following detailed description and upon referring to the drawings in which:

FIG. 1 is a bottom view of an existing safety helmet, showing the crown webbing layer;

FIG. 2 is a bottom view of an existing safety helmet, showing permanent mounting points;

FIG. 3 is a bottom view of the helmet of the present application;

FIG. 4 is a bottom view of the helmet space frame and headband of the present application, removed from the helmet shell;

FIG. 5 is a side view of the helmet space frame and headband, removed from the helmet shell and adjusted to a model head;

FIG. 5A is a side view of an alternative embodiment of the helmet space frame and headband, removed from the helmet shell and adjusted to a model head;

FIG. 6 is a bottom view of the helmet impact attenuation liner of the present application, removed from the helmet shell;

FIG. 7 is a front view of the helmet of the present application;

FIG. 8 is a back view of the helmet of the present application;

FIG. 9 is a side view of the headband of the present application, adjusted to a model head, and an additional component mounted to the headband; and

FIG. 10 is an exploded view of the helmet, space frame and headband system the present application.

While the invention will be described in conjunction with the illustrated embodiments, it will be understood that it is not intended to limit the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, similar features in the drawings have been given identical reference numerals where appropriate. References to the left or right side and front or back of the helmet and system components are made with respect to the helmet and system situated on a wearer's head.

FIGS. 1 and 2 illustrate helmet designs known in the Prior Art and in use at present.

FIG. 3 illustrates a safety helmet 10, including a fitting and impact attenuation system in accordance with an embodiment of the present invention. The helmet shell 12 may be a standard helmet shell used in the military. Within the helmet 10, and as shown in FIG. 4, the fitting system includes a space frame 14 in accordance with an embodiment of the present application. The space frame 14 is a flexible system which, when affixed and conformed to the interior of the shell 12 and having a headband 16 attached, results in a system 10 that provides offset in the fore-aft and lateral directions with maximum comfort and helmet stability in the required directions. The use of impact attenuating material and a comfort pad, described below, also adds to the crown standoff. The space frame 14 may be made of any semi-rigid engineered plastic.

Arms of the space frame 14 extend from a central crown point 20 and may be mounted to an existing helmet shell 12 at the three permanent and pre-existing mounting points in a typical helmet configuration, namely, one mounting point 30 at the back of the helmet and two mounting points 32, 34 at the front sides of the helmet. For example, the back mounting arm 38 is attached to the mounting point 30 at the back of the helmet shell 12. Side mounting arms 40, 42 attach to the front side mounting points 32, 34. As seen in FIG. 4, the back mounting arm 38 and side mounting arms 40, 42 may be spaced equally about the central crown point 20. The spacing and location of the back mounting arm 38 and side mounting arms 40, 42 may be adapted to fit the permanent mounting points 30, 32, 34 of the helmet shell 12 in order to provide a retrofit helmet fitting and impact attenuation system for existing helmet shells. Alternatively, the spacing and location of the back mounting arm 38 and side mounting arms 40, 42 may be configured for a new or custom helmet shell 12 and mounting points. Additional arms such as a rear arm 44, front arm 46, left side arm 48 and right side arm 50 may extend from the central crown point 20. The arms 44, 46, 48, 50 may be spaced apart about 90 degrees, and situated between the back mounting arm 38 and side mounting arms 40, 42 to add further structure and support to the space frame 14. The arms 38, 40, 42 of the space frame are configured to constrain vertical movement of the headband 16 relative the helmet shell 12, while allowing for some adjustment and lateral movement of the headband 16.

As seen in FIG. 4, a left tab 52 and a right tab 54 also may extend from the left side arm 48 and right side arm 50, respectively and also may be attached to the helmet shell 12 at the front side mounting points 32, 34 adding further support for the headband 16.

The space frame 14 is semi-permanently affixed to the helmet shell 12 using the existing mounting screws or any other suitable fastener and requires tools to detach from the helmet shell 12, thus deterring a wearer from removing or modifying the space frame component. The space frame 14 may be removed, however, for any necessary replacement, cleaning or repair.

As shown in FIGS. 4, 5 and 5A, the headband 16 is removably attached to the free ends of one or more arms 44, 46, 48, 50 of the space frame 14 using Velcro™ or other suitable means. The headband 16 may be a circular band fastened to the space frame 14 or an open strip of material fastened to the space frame 14 with the ends of the headband spaced apart to accommodate the size of the wearer's head. As illustrated in FIG. 5, an adjustable connection means, such as a dial mechanism 82, may be integrated with the ends of the headband 16. Alternatively, as can be appreciated from FIGS. 4 and 5A, the ends of the headband may be attached and adjusted at a headband rear tab 56 at the end of the space frame rear arm 44. In the configuration of FIG. 5A, the dial mechanism 82 may be used in addition to the connection of the headband 16 at the rear tab 56. The use of a rear tab 56 allows for retrofit to existing helmet shells 12. Additionally, the headband 16 and rear tab 56 may be adjusted to a loose but comfortable configuration for the wearer and as needed, the dial mechanism 82 may be adjusted quickly to tighten and secure the helmet 10. The use of the rear tab 56 and dial mechanism 82 provides further accommodation for variations in head sizes and shapes. In both embodiments of FIGS. 5 and 5A, the dial mechanism 82 also provides added stability to the system 10 as it engages a lower portion of the wearer's head.

An additional front tab 60 may be provided at the front of the headband 16 and space frame 14 as shown in FIG. 4. The front tab 60 is affixed with the side arms 40, 42 and respective left and right tabs 52, 54 to the helmet shell 12. The front tab 60 provides additional lateral stability for the headband 16 as well as sizing of the headband 16 to accommodate the forehead of the user. Adjustment of the headband 16 is required to accommodate the differing head circumferences and shapes of wearers' heads.

The headband 16 may be removed from the space frame 14 and thus from the helmet to be cleaned, replaced and readjusted without the need for additional tools. The headband 16 typically is constructed of semi-rigid plastic and covered with a material such as a fabric backed with foam or other compliant layer. Since the space frame 14 is attached to the outer side of the headband 16, the headband 16 provides a comfortable fit for the wearer and the wearer is not irritated by other straps or gear, such as the multiple loops of the crown webbing layer in the prior art.

FIG. 5 illustrates the space frame 14 and headband 16 on the head of the helmet wearer, separate from the helmet shell 12. The space frame rear arm 44, front arm 46, left side arm 48 and right side arm 50 are attached to the headband 16 while the space frame back mounting arm 38, side mounting arm 40, and side mounting arm 42 (not shown) are attached to the helmet shell 12. Arms 38, 40 and right tab 54 are shown in a free, unattached position in FIG. 5A. A dial mechanism 82, described below, also may be integrated with the headband 16. As can be appreciated from FIGS. 4, 5 and 5A, the headband 16 may be attached to a space frame 14 which is already affixed to the helmet shell 12. Alternatively, prior to affixing the space frame 14 to the shell 12, the space frame 14 may be attached to the headband 16, allowing the wearer to adjust the headband 16, prior to assembling the helmet 10.

The semi-rigid space frame 14 provides an appropriate vertical displacement between the wearer's head and the helmet shell 12 and maintains the proper positioning of the wearer's head within the helmet shell 12. As well, as seen in FIG. 5, the headband contours to accommodate the wearer's head and ears and to provide clearance for additional items, such as headphones. Thus, as long as the location of the three attachment points are maintained, the space frame 14 allows the headband to be provided in different sizes and shapes to accommodate variations in the size and shape of the wearer's head. The headband 16 need not conform to the multiple loops and attachment to the crown webbing layer of the previous helmet.

Thus, the space frame 14 provides for proper positioning of the headband and ultimately the wearer's head, within the helmet 10. The removal, readjustment and reattachment of the headband 16 do not interfere with this positioning. The space frame 14 also provides a degree of mechanical constraint between the headband 16 and the wearer's head. By attaching the headband 16 to the helmet shell 12 via the space frame 14, the headband 16 is prevented from moving vertically relative to the helmet shell 12, thus increasing the helmet's stability. The space frame 14 allows some lateral movement of the headband (and thus the wearer's head) relative to the helmet shell 12.

The space frame 14 allows for an impact attenuation liner layer 70 to be inserted between the helmet wearer and the helmet shell 12. FIG. 6 illustrates the impact attenuation liner 70 removed from the helmet shell 12. The impact attenuation liner 70 may be installed after the installation of the space frame 14 and the arms of the impact attenuation liner may be adjusted around and behind the arms of the space frame 14. As seen in FIG. 7, the arms of the impact attenuation liner 70 may be adjusted behind the back mounting arm of the space frame 14. Optionally, the impact attenuation liner 70 may be adjusted and located behind the arms 44, 46, 48, 50 attaching to the headband 16. The impact attenuation liner 70 may be removably installed or affixed to the interior of the helmet shell 12 with double-sided tape or other suitable means. Optionally, padding such as a crown padding insert 72 may be attached to the impact attenuation liner or space frame for the wearer's additional comfort and for vertical placement of the helmet on the head.

The impact attenuation material may comprise expanded polypropylene (EPP), EPS, Gecet™, vinyl nitrile (VN), polyurethane, polypropylene, viscoelastic and other foams or other impact attenuating materials such as Brock™, Skydex™, Zorbium™, or any other suitable material which meets the impact protection requirements. As shown in FIGS. 6 and 7, the impact attenuation liner 70 may be contoured and shaped to provide comfort and ventilation to the helmet wearer. The impact attenuation liner may be provided as one continuous layer which reduces the number of parts required to complete a retrofit of a helmet shell 12 and which removes the possibility that one or more individual impact attenuation components may be removed by the helmet wearer, thus inadvertently compromising safety. Additionally, the impact attenuating liner may be permanently moulded in the same shape of the helmet shell as is common for injection moulded materials such as expanded bead foams (EPS, EPP, Gecet™). The aforementioned materials are for reference only and the liner 70 is not limited to these materials.

As seen in FIGS. 3, 7 and 8 the helmet includes retention straps 90, 92 affixed to the helmet shell 12 at the permanent mounting points 30, 32, 34. The straps may be adjustable via traditional buckle arrangements or other suitable means to fit the helmet 10 to the individual wearer. As with previous helmets, the retention straps typically are affixed beneath the wearer's chin which is supported in further strapping or a chin cup 94, which is shown in FIG. 3.

In another aspect of the present invention, a yoke 80 may be provided at the back of the helmet 12 near the back mounting point 30 to provide separation between the joining of the straps at the back of the helmet. The yoke 80 is shown in FIG. 7, behind the headband 16 and within the helmet shell 12, so as to provide increased stability for the straps but without interfering with the fit of the helmet and the helmet wearer's comfort.

FIG. 8 illustrates the dial mechanism 82 located at the rear of the helmet 10. As described above, the headband adjustment dial mechanism 82 may easily be loosened for regular wear or tightened for user-specific requirements. In both cases, this adjustment does not interfere with the positioning of the wearer's head relative to the helmet shell 12 because this positioning is maintained by the space frame 14. Thus, the arrangement of the space frame 14 and headband 16 allow for further adjustment of the helmet 10 to suit the wearer's needs without compromising safety.

FIG. 9 illustrates the headband 16 according to the embodiments described herein, adjusted to a wearer's head (shown as a model head) and supporting an additional component such as an earphone 98 and microphone or mouthpiece 100, as illustrated (other equipment, not shown, is contemplated). Previously, these components were supported by other straps or means fitted to the wearer's head, under the helmet. Thus, the additional straps were a source of discomfort and the helmet also interfered with the proper positioning of the earpiece and microphone. With the semi-rigid space frame 14 and headband 16 of the present invention, such devices may be supported by the headband 16 itself, thus eliminating the need for additional strapping and components in an area where space is limited and eliminating a potential source of discomfort for the wearer. Such devices may be removably attached to the headband 16 as required. Because the headband 16 is positioned relative to the helmet shell 12 by the space frame 14, the attachment of such additional equipment to the headband 16 also does not interfere with the positioning of the headband 16 relative to the helmet 10.

FIG. 10 illustrates the helmet fitting, retention and impact attenuation systems according to the present invention in an exploded view. The space frame 14, headband 16, impact attenuation liner 70 and crown padding insert 72 are shown uninstalled from the helmet shell 12. As discussed above, the space frame 14 is affixed to permanent mounting points on the helmet shell 12, after which the impact attenuation liner 70 may be inserted around the space frame 14 and within the spacing maintained between the space frame 14 and the helmet shell 12. The headband 16 may be attached to the space frame 14 prior to installation or after the space frame 14 is installed within the helmet shell 12.

Thus, it is apparent that there has been provided in accordance with the embodiments of the present invention a helmet fitting and impact attenuation system that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with illustrated embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the invention. 

1. A fitting and impact attenuation system for use in a helmet, comprising: a semi-rigid space frame comprising a plurality of arms extending from a central crown point wherein at least three of said arms are attachable to the helmet such that said space frame is releasably fixed to said helmet; a headband for receiving a head of a wearer, said headband releasably attachable to said space frame by one or more of said arms; and an impact attenuation layer, fixably mounted to an inside surface of said helmet, wherein said space frame maintains said headband in a fixed vertical configuration relative to said helmet.
 2. The system of in claim 1, wherein the plurality of arms comprises three arms attachable to the helmet and three arms releasably attachable to the headband.
 3. The system of in claim 2, wherein the three arms attachable to the helmet comprise: a back mounting arm; and two side mounting arms, the three arms being approximately equally spaced about the central crown point of the space frame.
 4. The system of claim 3, wherein the three arms releasably attachable to the headband comprise: a front arm, extending from the central crown point between the two side mounting arms and opposite the back mounting arm; a left arm; a right arm; and each of the left and right arms being spaced about ninety degrees from the front arm and about ninety degrees from the back mounting arm.
 5. The system of claim 4 further comprising a rear arm extending from the central crown point below and parallel to the back mounting arm.
 6. The system of claim 5 wherein the headband is releasably attachable to free ends of the front arm, right arm, rear arm and left arm.
 7. The helmet fitting and impact attenuation system of claim 6 further comprising a rear tab extending from and perpendicular to the free end of the rear arm.
 8. The system of claim 7 wherein the headband further comprises a strip of material having two free ends, the free ends of the headband being releasably attachable to the rear tab.
 9. The system of claim 4 further comprising a right tab extending from and perpendicular to a free end of the right arm and a left tab extending from and perpendicular to a free end of the left arm, a portion of the right tab and a portion of the left tab being releasably attachable to the headband.
 10. The system of claim 9 wherein the right tab extends perpendicularly from the right arm to an adjacent side mounting arm, the right tab and the adjacent side mounting arm being attachable to a first helmet mounting point and wherein the left tab extends perpendicularly from the left arm to an adjacent side mounting arm, the left tab and the adjacent side mounting arm attaching to a second helmet mounting point.
 11. The system of claim 9 wherein the headband is releasably attachable to the free end of the front arm, the right tab, the free end of the rear arm and the left tab.
 12. The system of claim 1 wherein said space frame is configured to permit lateral movement of the headband relative to said helmet.
 13. The system of claim 1 further comprising a crown padding layer releasably attachable to the impact attenuation liner.
 14. A helmet comprising: a helmet shell; a semi-rigid space frame comprising a plurality of arms extending from a central crown point wherein at least three of said arms are attachable to said helmet shell such that said space frame is releasably fixed to said helmet shell; a headband for receiving a head of a wearer, said headband releasably attachable to said space frame by one or more of said arms; and an impact attenuation layer, fixably mounted to an inside surface of said helmet shell, wherein said space frame maintains said headband in a fixed vertical configuration relative to said helmet shell.
 15. The system of in claim 14, wherein the plurality of arms comprises three arms attachable to the helmet shell and three arms releasably attachable to the headband.
 16. The system of in claim 15, wherein the three arms attachable to the helmet shell comprise: a back mounting arm; and two side mounting arms, the back mounting arm and two side mounting arms being approximately equally spaced about the central crown point of the space frame; and wherein the three arms releasably attachable to the headband comprise: a front arm, extending from the central crown point between the two side mounting arms and opposite the back mounting arm; a left arm, spaced about ninety degrees from the front arm and spaced about ninety degrees from the back mounting arm; and a right arm, spaced about ninety degrees from the front arm and spaced about ninety degrees from the back mounting arm.
 17. The system of claim 16 further comprising a rear arm extending from the central crown point below and parallel to the back mounting arm.
 18. The system of claim 17 further comprising a crown padding layer releasably attachable to the impact attenuation liner. 